Terpolymers containing organosilicon side chains

ABSTRACT

A terpolymer containing 20 to 70 mole percent of an acid labile repeating unit, 3 to 40 mole percent of an acrylonitrile based repeating unit and a repeating unit containing silicon side chains. The silicon side chain repeating unit is provided in sufficient amounts so that the terpolymer silicon content is 7 to 20 weight percent. The terpolymer is used primarily in the formulation of multilayer positive operating photoresists.

This is a continuation of application Ser. No. 08/682,171 filed Jul. 16,1996, now U.S. Pat. No. 5,886,117.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention concerns a new terpolymer with silicon-containingside chains, a radiation-sensitive composition based on this terpolymer,as well as two processes for the lithographic treatment of a substrateby means of these compositions and corresponding processes for theproduction of an object, particularly an electronics component.

2. Brief Description of Relevant Art

In recent years, the extent of integration of semiconductor componentshas been continually increasing. The resolution capacity that can beobtained with conventional deep-UV microlithography has thus reached itslimits. Normally, it is no longer possible to produce, on a substrate,conventional structures with dimensions of less than 0.25 μm, as isrequired for the production of particularly highly integratedelectronics components that have been targeted recently; these haveminimal dimensions down to approximately 0.12 μm. In order to be able toresolve sufficiently, in an optical manner, such fine structuralelements, particularly short-wave radiation must be utilized, whichgenerally has a wavelength between 190 and 260 nm.

Today's conventional deep-UV photoresistant materials, however, arepoorly suitable for such radiation. These materials are usually based onphenolic resins as binders, for example, on novolak resins or onpolyhydroxystyrene derivatives, which show a strong absorption atwavelengths below 260 nm, due to their aromatic structural elements.However, this leads to the fact that, with the use of such radiation,the side walls of the finished developed resist structures do not formthe targeted right angle, but rather form a more or less oblique anglewith the substrate or the resist surface, which nullifies the obtainingof optical resolution as a consequence of the use of shortwaveradiation.

Photoresists without a sufficiently high proportion of aromaticcomponents, e.g., resists based on methacrylate resins, have provensufficiently transparent for radiation below 260 nm, but they do nothave the stability in plasma etching that is customary for resists basedon phenolic resins; plasma etching is a principal method for producingmicrostructures on silicon substrates. The plasma etching stability, asis known, is essentially based on the aromatic groups in these resists.

There have also been various solutions proposed for this problem. Onesolution is offered by the use of a special multilayer technique. First,an initial resin coating, commonly called a planarizing layer, isintroduced onto the substrate, and this layer must not bephotostructurable. A second coating, a covering layer that can bephotostructured, which contains an organosilicon component instead of acomponent with a high content of aromatic compounds, is introduced ontothis first layer. The substrate coated in this way is selectivelyexposed, i.e., in an image-forming way, in the conventional manner andthen treated with a suitable developer, so that a desired image-formingstructure is generated in the covering coating that can bephotostructured. A subsequently conducted treatment in oxygen plasmaleads to the fact that the organosilicon compounds contained in it areoxidized to silicon oxides, at least on the surface, and these oxidesform a closed etching barrier for the oxidative decomposition of theorganic material that lies underneath, particularly the planarizinglayer, while the planarizing layer is removed completely in an oxidativemanner on those places that are not coated by the silicon-containingcovering layer.

Various compositions that can be photostructured and containorganosilicon components, which are suitable for the above-givenlithographic process, are described, for example, in WO-A-94/11,788. Inone type, this involves a composition based on a substance that formsacid under the effect of actinic radiation (in the following, suchcompounds will also be called photo acid generators) and a copolymer asbinder. The copolymer comprises repeating structural units with atomgroups that cleave under the catalytic effect of acid, and in this waycan bestow solubility to the binder in aqueous-alkaline developers, andis also comprised of repeating structural units that containorganosilicon side chains. A typical corresponding copolyer has thefollowing structure: ##STR1##

Compositions such as these, however, are still capable of improvement.For example, their heat form stability is still insufficient for certainrequirements, because a softening might occur during treatment in oxygenplasma and as a consequence, the covering layer may soften and flow,which can lead to an imprecise formation of the etching barrier andconsequently to an imprecise transfer of the desired structure onto thesubstrate. Further, the named polymers also very strongly absorbradiation of 193 nm wavelength, due to their content of aromaticcompounds.

BRIEF SUMMARY OF THE INVENTION

The present invention has the task of making available a positivelyoperating, chemically reinforced photoresist containing organosiliconcomponents, particularly for use for multilayer techniques, and thisphotoresist will be characterized by improved heat form stability and ahigher T_(g) value (higher glass transition point). It has been shownthat this can be achieved by the use of a specific organosiliconterpolymer as the binder for the etching resist.

The subject of the present invention is thus a terpolymer containing 20to 70 mole percent of repeating structural units of formula (I) and 3 to40 mole percent of repeating structural units of formula (II): ##STR2##as well as repeating structural units of formula (III): ##STR3## wherebyA indicates a direct single bond or a group of the formula: ##STR4## R₁indicates a hydrogen atom or a methyl group, R₂ indicates a 2-furanyloxyor 2-pyranyloxy group or a group of the formula: ##STR5## R₃ indicates agroup of the formulas: --COOH or --CN,

R₄ indicates a group selected from the groups of formulas: ##STR6## R₅indicates a C₁ -C₆ alkyl group or a phenyl group, R₆ indicates a C₁ -C₆alkyl group or a phenyl group,

R₇ indicates a C₁ -C₆ alkyl group or a phenyl group,

Y indicates a hydrogen atom or a chlorine atom or a methyl group,

Z indicates a group of the formula --OSi(CH₃)₃,

m indicates 1, 2 or 3,

n indicates 3 minus m, and

p indicates 0, 1, 2 or 3

and whereby

as many structural units of formula (III) are contained in theterpolymer such that its silicon contents amounts to 7 to 20 weightpercent.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

The molecular weight (weight average M_(w)) of the terpolymers of theinvention appropriately lies between 5,000 and 200,000 and preferablybetween 8,000 and 50,000.

If residue R₂ corresponds to a 2-furanyloxy or a 2-pyranyloxy group,then these are preferably unsubstituted. They may, however, also besubstituted, particularly by one or more C₁ -C₄ alkyl groups or C₁ -C₄alkoxy groups.

The residue R₁ preferably corresponds to a methyl group.

The residue R₂ preferably corresponds to a group of formulas: ##STR7##especially to the group ##STR8## Preferably, residue R₃ indicates--COOH. R₅, R₆ and R₇ indicate C₁ -C₆ alkyls, e.g., methyl, ethyl,n-propyl, i-propyl, butyl residues, pentyl or hexyl residues.

Further, terpolymers are preferred according to the invention, in whichp amounts to 1, 2, or most preferably to 3.

Preferably, the terpolymers of the invention contain 3 to 35 molepercent of repeating structural units of formula (II). Thus, they mayhave, for example,

3 to 35 mole percent of repeating structural units of formula (II), and

15 to 30 mole percent of repeating structural units of formula (III),whereby repeating structural units of formula (I) form the balance to100 mole percent and make up for example, 50 to 70 mole percent.

Most particularly preferred are terpolymers of the invention, in whichR₂ corresponds to a group of formula ##STR9## R₃ corresponds to a groupof formula

    --COOH

and

R₄ corresponds to a group of formula

    --(CH.sub.2).sub.3 -Si[OSi(CH.sub.3).sub.3 ].sub.3

particularly if these termpolyers 3 to 31 mole percent repeatingstructural units of formula (II), 10 to 30 mole percent of repeatingstructural units of formula (III), whereby repeating structural units offormula (I) form the balance to 100 mole percent.

The terpolymers of the invention may be produced from the corresponding(meth)acrylate and/or vinyl ether monomers with the application ofconventional thermal or even radiation-induced polymerization methodsknown to the expert. Conventional polymerization methods are, forexample, mass polymerization or solvent polymerization or also emulsion,suspension or precipitation polymerization.

The terpolymers of the invention represent a valuable formulationcomponent for radiation-sensitive compositions, as for chemicallyreinforced positive-operating photoresist compositions. The inventionthus also has as a subject a radiation-sensitive composition thatcontains the above-described terpolymers as well as a substance, whichforms acid under the effect of actinic radiation of a wavelength below300 nm and preferably below 260 nm. The radiation-sensitive compositionof the invention appropriately contains 80 to 99.9, preferably 90 to99.5 weight percent of the terpolymer of the invention, as well as0.1-20, preferably 0.5-10 weight percent of the photo acid generator,whereby the latter data refer to the total amount of these twocomponents in the composition.

All known compounds can be used as the photo acid generator, as long asthey form acid under the effect of actinic radiation of a wavelengthbelow 300 nm. A large number of such compounds is named, e.g., in EP-A-0601,974 (=U.S. Pat. No. 5,369,200), whose description will also be acomponent of this description. Preferred radiation-sensitive acid donorsare onium salts, such as diazonium, sulfonium, sulfoxonium, and iodoniumsalts, as well as disulfones.

Preferably preferred are sulsonium salts of the formula:

    (Ar.sub.1).sub.q (Z.sub.1).sub.r (Z.sub.2).sub.s S.sup.+ X.sub.1.sup.-

in which

Ar₁ is unsubstituted phenyl, naphthyl, or phenyl-COCH₂ -- or thesecompounds substituted by halogen, C₁ -C₄ alkyl, C₁ -C₄ alkoxy, --OHand/or nitro-substituted,

Z₁ is C₁ -C₆ alkyl or C₃ -C₇ cycloalkyl, and Z₂ is tetrahydrothienyl,tetrahydrofuryl or hexahydropyryl,

q stands for 0, 1, 2 or 3

r stands for 0, 1 or 2, and

s stands for 0 or 1, whereby the sum of q+r+s amounts to 3, and X₁ ⁻ isa chloride, bromide, or iodide anion, BF₄ ⁻, PF₆ ⁻, AsF₆ ⁻, SbF₆ ⁻ orthe anion of an organic sulfonic acid or carboxylic acid.

Phenyl, naphthyl and phenacyl Ar₁ groups may also be multiplysubstituted, or preferably singly substituted, for example, by Cl, Br,methyl, methoxy, --OH or nitro. Particularly preferred, these residuesare unsubstituted. Z₁ is preferably C₁ -C₄ alkyl, especially methyl orethyl. Preferably, q is 2 or 3, r is 1 or zero and s is zero, andparticularly, q is the number 3 and r and s are zero. Most particularlypreferred, Ar₁ is unsubstituted phenyl and q is 3.

If X₁ ⁻ represents the anion of an organic sulfonic acid or carboxylicacid, then it may involve anions of aliphatic, cycloaliphatic,carbocyclic-aromatic, heterocyclic-aromatic or araliphatic sulfonic orcarboxylic acids. These anions may be substituted or unsubstituted.Sulfonic and carboxylic acids with small nulceophilia are preferred, forexample, partially fluorinated or perfluorinated derivatives orderivatives substituted in the neighboring position to the respectiveacid group. Examples of substituents are halogens, such as chlorine, andparticularly fluorine, alkyl, such as methyl, ethyl or n-propyl, oralkoxy, such as methoxy, ethoxy or n-propoxy.

Preferably X₁ ⁻ is the monovalant anion of an organic sulfonic acid,particularly a partially fluorinated or perfluorinated sulfonic acid.These anions are characterized by a particularly small nucleophilia.

Special examples of suitable sulfonium salts are triphenyl sulfoniumbromide, triphenyl sulfonium chloride, triphenyl sulfonium iodide,triphenyl sulfonium hexafluorophosphate, triphenyl sulfoniumhexafluoroantimonate, triphenyl sulfonium hexafluoroarsenate, triphenylsulfonium trifluoromethane sulfonate, diphenylethyl sulfonium chloride,phenacyldimethyl sulfonium chloride, phenacyltetrahydrothiopheniumchloride, 4-nitrophenacyltetrahydrothiophenium chloride, and4-hydroxy-2-methylphenylhexahydrothiopyrylium chloride. Particularlypreferred is triphenyl sulfonium trifluoromethane sulfonate (triphenylsulfonium triflate).

Particularly preferred, sulfonium compounds of the above formula areused, in which

Ar₁ indicates phenyl,

q is the number 3,

r and

s are zero, and

X₁ ⁻ represents SbF₆ ⁻, AsF₆ ⁻, PF₆ ⁻, CF₃ SO₃ ⁻, C₂ F₅ SO₃ ⁻, n-C₃ F₇SO₃ ⁻, n-C₄ F₉ SO₃ ⁻, n-C₆ F₁₃ SO₃ ⁻, n-C₈ F₁₇ SO₃ ⁻, C₆ F₅ SO₃ ⁻.

The photoresists of the invention may also contain suitable conventionaladditives in conventional quantities, e.g., of an additional 0.01 to 40weight percent, with respect to the total quantity of terpolymer andphoto acid generator, such as, e.g., basic additives (lacqueradditives), for example 2-methylimidazole, triisopropylamine,4-dimethylaminopyridine or 4,4'-diaminodiphenyl ether, or alsostabilizers, pigments, colorants, fillers, bonding agents, levelingagents, wetting agents and softeners.

Preferably, the photoresist compositions are dissolved in a suitablesolvent for the application. The selection of the solvent and theconcentration are primarily directed according to the type ofcomposition and according to the coating process. The solvent will beinert, i.e., it will not enter into any chemical reaction with thecomponents and it can be removed again after coating during drying.Suitable solvents are, e.g., ketones, ethers and esters, such as methylethyl ketone, 2-heptonone, cyclopentanone, cyclohexanone,γ-butyrolactone, ethyl pyruvate, diethylene glycol dimethyl ether,2-methoxyethanol, 2-ethoxy ethanol, 2-ethoxyethyl acetate,1-methoxy-2-propyl acetate, 1,2-dimethoxyethane, acetic acid ethylester, and 3-methoxymethyl propionate, or mixture of these solvents.

The resist formulations according to the invention (radiation-sensitivecompositions) may be produced, for example, by mixing of the individualcomponents with stirring, whereby a homogeneous solution is obtained.

The compositions of the invention are suitable as positive photoresists,whereby both a single layer as well as a multilayer technique can beapplied. In this application, a positive photoresist is understood to bea composition, which dissolves better in an aqueous-alkaline solutionafter radiation, and a subsequent heat treatment, if needed.

The invention thus also has as a subject a process for the lithographictreatment of a substrate by means of a multilayer technique, in whichthe substrate:

a1) is provided with a first coating of a film-forming organic material,

b1) a second coating containing a terpolymer of the invention and asubstance that forms acid under the effect of actinic radiation of awavelength below 260 nm, is introduced on this first coating,

c1) the thus-coated substrate is irradiated in an image-forming way withwith radiation of a wavelength of 248 to 254 or of 193 nm, to which thephoto acid generator is sensitive,

d1) is subjected to a heat treatment,

e1) is treated with an aqueous alkaline developer solution, until theirradiated regions of the second coating are removed, and

f1) after this is treated with an oxygen-containing plasma until thefirst coating is completely removed on those places where it is notcovered by the second coating.

In addition, the invention has as a subject a process for thelighographic treatment of a substrate by means of a single-layertechnique, in which on the substrate

a2) is introduced a coating, containing a terpolymer of the inventionand a photoinitiator, which forms acid under the effect of actinicradiation of a wavelength below 260 nm,

b2) the thus-coated substrate is irradiated in an image-forming way withradiation to which the photoinitiator is sensitive, particularly withradiation of a wavelength of 248 to 254 nm or of 193 nm,

c2) is subjected to a heat treatment, and

d2) is treated with an aqueous alkaline developer solution until theirradiated regions of the second coating are removed.

Practically all film-forming organic polymers can be used as thefilm-forming organic material for the first coating (planarizing layer)with the use of the multilayer technique. Particularly preferred arephenolic resins, particularly novolak resins, such as formaldehydecresol or formaldehyde phenol novolaks, as well as polyimide resins, andpoly(meth)acrylate resins. The planarizing layer is generally 0.5 to 1μm thick. The resin is first dissolved in a suitable solvent and thenintroduced by the usual coating processes onto the substrate, e.g., bydipping, blade coating, painting, spraying, particularly byelectrostatic spraying, and reverse-role coating, and above all byspinning.

After the first layer is dried, the second coating, containing aterpolymer of the invention, a substance that forms acid under theeffect of actinic radiation of a wavelength below 300 nm, preferablybelow 260 nm, as well as other additives, if needed, is introduced ontothe first coating. The second coating may also be realized with anyconventional coating process, for example, one of those named above, buthere also spin coating is particularly preferred. The covering layer isappropriately approximately 0.2 to 0.5 μm thick.

For the production of relief structures, the thus-coated substrate isthen selectively exposed, i.e., to form the image. Exposure ispreferably produced with actinic radiation of a wavelength of 190-300nm, particularly of 190 to 260 nm. All known sources of the respectiveradiation can be utilized in principle for irradiation, for example,mercury high-pressure lamps, but particularly excimer lasers, such asthe krypton fluoride laser with radiation of 248-nm wavelength or theargon fluoride excimer laser with 193-nm radiation. The image-formingirradiation is produced either by means of a mask, preferably achromium-quartz mask, or--when laser exposure devices are used--also bymoving the laser beam in a computer-controlled manner over the surfaceof the coated substrate and thus the image is produced. Here, the highsensitivity of the photoresist materials of the invention is veryadvantageously noticeable in that it permits high writing speeds atrelatively low intensities. The high sensitivity of the resist is alsoof advantage for exposure by means of steppers, where very shortexposure times are desired.

The process of the invention also encompasses, between selectiveirradiation and treatment with a developer, a heating of the coating asa further process measure. By means of this heat treatment, theso-called "post-exposure bake", a practically complete reaction of theresist material, is obtained in an especially rapid time. The time andtemperature of this post-exposure bake may vary within broad regions andessentially depend on the composition of the resist, particularly by thetype of its acid-sensitive components, and the type ofradiation-sensitive acid donor used, as well as the concentrations ofthese two components. Commonly, the exposed resist is subjected toseveral seconds up to several minutes of temperatures of approximately50-150° C.

After the image-forming exposure and heat treatment of the materialconducted as needed, the irradiated spots of the covering coating thatare better soluble in aqueous alkaline as a consequence are dissolvedout with an aqueous-alkaline developer, i.e., with an aqueous solutionof bases to which small quantities of organic solvents or their mixturesmay also be added as needed.

Particularly preferred as developers are aqueous alkaline solution, asthey are also utilized for the development of conventional novolaknaphthoquinone diazide positive resist coatings. These include, e.g.,aqueous solutions of alkali metal silicates, phosphates, hydroxides, andcarbonates, but particularly tetraalkylammonium hydroxide solutions,such as e.g., tetramethylammonium hydroxide solution, which is free ofmetal ions. Still smaller quantities of wetting agents and/or organicsolvents may also be added to these solutions. Typical organic solvents,which may be added to the developer fluids, are, for example,cyclohexanone, 2-ethoxyethanol, toluene, acetone, isopropanol orethanol, as well as mixtures of two of more of these solvents.

After this, the thus-treated workpiece is treated with an oxygen plasma,whereby a closed silicon oxide layer is formed within several seconds,at least in the uppermost regions of the covering coating oforganosilicon components in the covering layer, and this silicon oxidelayer protects the regions of the organic material lying underneathagainst an attack of oxygen plasma. Treatment with the oxygen plasma iscontinued until the substrate is completely free in those places wherethe covering coating has been removed beforehand by means of thedeveloper. In general, an etching time of 5 to 15 minutes is sufficientfor this purpose.

The substrate can finally be subjected to a conventional structuringtreatment, e.g., a dry etching in halogen, CF₄, or oxygen plasma onthose places free of the coating. After this, the entire protectivecoating is removed from the substrate, e.g., by dissolving with asuitable solvent, after which the depicted process cycle is repeated, ifneeded, in order to produce further structures on the substrate.Therefore, a process for the production of an object, particularly anelectronic component, comprising the above-depicted process for thelithographic treatment of a substrate forms another subject of theinvention.

The present invention is further illustrated by the following Examples.All parts and percentages are by weight and all temperatures are degreesCelsius unless explicitly stated otherwise.

EXAMPLES Example 1

Production of a terpolymer of methacrylic acid tetrahydro-2H-pyranylester, methacrylic acid, and methacryloxypropyl-tris(trimethylsiloxy)silane.

A solution of 6.38 g (37.5 mmoles) of methacrylic acidtetrahydro-2H-pyranyl ester, 6.33 g (15 mmoles) ofmethacryloxypropyl-tris(trimethylsiloxy) silane, 1.95 g (23 mmoles) ofmethacrylic acid, 0.16 g of azobisisobutyronitrile and 0.1 g of1-dodecanethiol in 105 ml of tetrahydrofuran are stirred for 20 secondsunder a nitrogen atmosphere at a temperature of 75° C. in a 250-mlround-bottomed flask with a magnetic stirrer. After cooling, thereaction solution is precipitated by addition of one liter of water. Theformed precipitate is filtered and dried in high vacuum (4×10⁻⁶ bars),whereby 11.7 g (78% of the theoretical) of a white powder are obtained.

GPC (polstyrene standard): M_(w) =11,950; M_(n) =4,250; M_(w) /M_(n)=2.8.

TGA (heating rate of 10° C./min.): weight loss of 24.1% between 110 and200° C.

UV Absorption of a 0.45 μm thick film, produced, as described below, at193 nm: 0.17.

Example 2

A resist solution is prepared by dissolving 0.985 g of the terpolymer ofExample 1, 10 mg of triphenyl sulfonium triflate, and 0.5 mg ofdimethylaminopyridine in 5 ml of 1-methoxy-2-propyl acetate. Thissolution is spun at 4,000 rpm onto a 3-inch silicon wafer. After thesubsequent 1-minute drying at 100° C., a film results with a layerthickness of 0.5 μm. This film is exposed by means of a mercury vaporlamp of the type Ushio UXM-502 MD through a narrow-band interferencefilter and a chromium quartz mask with a radiation of 254 nm (dose of 20mJ/cm²). Then the wafer is heated to 120° C. for one minute on a hotplate and then developed in a 0.131 N solution of tetramethyl-ammoniumhydroxide in water, whereby the previously exposed zones of the resistfilm go into solution and those that are not exposed remain on thesubstrate.

Example 3

The resist solution of Example 2 is spun at 6,000 rpm onto a 4-inchsilicon wafer, which has already been coated with an 0.9 μm thick layerof a novolak film (produced by spinning a solution of a novolak with a28 mole percent cresol component (Novolak® P28 of OCG MicroelectronicMaterials, Inc. (OCG) of Norwalk, Conn., U.S.A.) in cyclopentanone andsubsequent 30-minute heating to 250° C.). After heating on the hot plate(1 minute; 100° C.), a 0.25-μm thick covering film results. The wafercoated in this way is now exposed to form an image with a Canon FPA 4500illumination device through a mask with radiation of a wavelength of 248nm and then is again heated for one minute on a hot plate to atemperature of 100° C. After this, it is first developed with a 0.131 Nsolution of tetramethyl-ammonium hydroxide in water, whereby the maskstructures are imaged in the covering layer as the relief. Then thestructures are treated in oxygen plasma (50 watts, 2 pascals ofpressure, 40 cm³ /min oxygen flow), produced with a device of theAlcatel Company, whereby the substrate is fully laid free on the placesof the multilayer coating that are free of the covering layer.Structures (equidistant lines and intermediate spaces) of 0.3 μm may beresolved with vertical wall profiles and without residue on thesubstrate.

Example 4

A silicon wafer coated analogously to Example 3 is contact-exposedthrough a chromium-quartz mask (0.5 μm as the smallest mask structures)with radiation of a wavelength of 193 nm, produced with a Lambda-PhysicsLPF 205 excimer laser. The dose amounts to 26 mJ/cm². After this, it isheated and developed, as in Example 3. The 0.5 μm structures(equidistant lines/intermediate spaces) are imaged with vertical wallprofiles.

Example 5

Production of a terpolymer of methacrylic acid tetrahydro-2H-pyranylester, methacrylic acid and methacryloxypropyltris(trimethylsiloxy)silane.

A solution of 2.13 g (12.5 mmoles) of methacrylic acidtetrahydro-2H-pyranyl ester, 2.11 g (5 mmoles) ofmethacryloxypropyltris(trimethylsiloxy)silane, 0.65 g (7.6 mmoles) ofmethacrylic acid, 0.08 g of azobisisobutyronitrile, and 0.05 g of1-dodecanethiol in 35 ml of tetrahydrofuran is stirred with a magneticstirrer in a 100-ml round-bottomed flask for 20 hours under a nitrogenatmosphere at a temperature of 75° C. After cooling the reactionsolution, precipitation is produced by the addition of 500 millilitersof water. The formed precipitate is filtered off and dried under highvacuum (4×10⁻⁶ bars) whereby 3.0 g (61% of the theoretical) of a whitepowder are obtained.

GPC (polstyrene calibration standard): M_(w) =13,260; M_(n) =6,290;M_(w) /M_(n) =2.1.

TGA (heating rate of 10° C./min.): weight loss of 24.1% between 110 and210° C.

UV Absorption at a 193 nm of a 0.45-μm thick film, produced by spinninga solution of the polymer in cyclopentanone and subsequent one-minutedrying at 100° C.:0.17.

Example 6

Production of a terpolymer of methacrylic acid t-butyl ester,methacrylic acid, and methacryloxypropyl-tris(trimethylsiloxy)silane.

A solution of 3.56 g (25 mmoles) of methacrylic acid t-butyl ester, 4.22g (10 mmoles) of methacryloxypropyl-tris(trimethylsiloxy)silane, 1.29 g(15 mmoles) of methacrylic acid, 0.16 g of azobisisobutyronitrile and0.1 g of 1-dodecanethiol in 64 ml of tetrahydrofuran is stirred with amagnetic stirrer in a 250-ml round-bottomed flask for 20 hours under anitrogen atmosphere at a temperature of 75° C. After cooling thereaction solution, it is precipitated by addition of 700 milliliters ofwater. The formed precipitate is filtered off and dried under highvacuum (4×10⁻⁶ bars), whereby 8.4 g (93% of the theoretical of a whitepowder are obtained.

GPC (polstyrene calibration standard): M_(w) =9,460; M_(n) =3,890; M_(w)/M_(n) =2.4.

TGA (heating rate of 10° C./min.): weight loss of 25.8% between 165 and280° C.

Example 7

The resist solution of Example 2 is spun at 6,000 rpm onto a 4-inchsilicon wafer, which has already been coated with a 0.6-μm thick layerof a novolak film (produced by spinning a solution of a novolak with 28mole % cresol component (Novolak® P28 of OCG) in cyclopentanone andsubsequent 30-minute heating at 250° C. After heating on the hot plate(1 minute; 100° C.), a 0.25-μm thick covering film results. Thethus-coated wafer is now exposed in an image-forming manner with a SVGLMicrascan Stepper prototype (installed at MIT Lincoln Laboratories,Lexington, Mass., U.S.A.) with a lens of numerical opening of 0.5 at awavelength of 193 nm (irradiation dose of 24 mJ/cm²) and then heated foranother 1 minute with a hot plate at a temperture of 100° C. After this,it is developed first with a 0.0016 N solution of tetramethylammoniumhydroxide in water, whereby mask structures are formed as a relief inthe covering layer. After this, the structures are treated in oxygenplasma (50 watts, 2 pascals of pressure, 40 cm³ /min oxygen flow),produced by a device of the Alcatel Company, whereby the substrate isfully laid free at the places of the multilayer coating that are free ofthe covering layer. Structures (equidistant lines and intermediatespaces) of 0.175 μm may be resolved with vertical wall profiles andwithout residue on the substrate.

Example 8

A resist solution is prepared by dissolving 0.985 g of the terpolymer ofExample 6, 10 mg of triphenylsulfonium triflate and 0.5 mg ofdimethylaminopyridine in 5 ml of 1-methoxy-2-propyl acetate. Thissolution is spun at 6,000 rpm onto a 3-inch silicon wafer, which hasalready been coated with a 0.9-μm thick layer of a novolak film(produced by spinning a solution of a novolak with 28% mole cresolcomponent (Novolak® P28 of OCG) in cyclopentanone and subsequent30-minute heating at 250° C. After heating on the hot plate (1 minute;100° C.) a 0.25-μm thick covering film results. The thus-coated wafer isnow exposed in an image-forming manner by means of a mercury vapor lampof the type Ushio UXM-502 MD through a narrow-band interference filterand chromium quartz mask with radiation of a wavelength of 254 nm(irradiation dose of 20 MJ/cm²) and then heated for another 1 minutewith a hot plate at a temperature of 100° C. Then, it is developed firstwith a 0.026 N solution of tetramethylammonium hydroxide in water,whereby the mask structures are imaged as a relief in the coveringlayer. After this, the structures are treated in oxygen plasma (50watts, 2 pascals of pressure, 40 cm³ /min oxygen flow), produced by adevice of the Alcatel Company, whereby the substrate is completely laidfree at the places of the multilayer coating free of the covering layer.In this way, submicrometer structures can be resolved with vertical wallprofiles and without residue on the substrate.

Example 9

The resist solution from Example 8 is spun at 6,000 rpm onto a 4-inchsilicon wafer, which has already been coated with a 0.6-μm thick layerof a novolak film (produced by spinning a solution of a novolak with 28mole % cresol component (Novolak® P28 of OCG) in cyclopentanone andsubsequent 30-minute heating at 250° C. After heating on the hot plate(1 minute; 100° C.), a 0.25-μm thick covering film results. Thethus-coated wafer is now exposed in an image-forming manner with a SVGLMicrascan Stepper prototype (installed at MIT Lincoln Laboratories,Lexington, Mass., U.S.A.) with a lens of numerical opening of 0.5 at awavelength of 193 nm (irradiation dose of 24 mJ/cm²) and then heated foranother 1 minute with a hot plate at a temperature of 100° C. Afterthis, it is developed first with a 0.026 N solution oftetramethylammonium hydroxide in water, whereby the mask structures areimaged as a relief in the covering layer. After this, the structures aretreated in oxygen plasma (50 watts, 2 pascals of pressure, 40 cm³ /minoxygen flow), produced by a device of the Alcatel Company, whereby thesubstrate is completely laid free on the places of the multilayercoating that are free of the covering layer. Submicrometer structuresmay be resolved with vertical wall profiles and without residue on thesubstrate.

While the invention has been described above with reference to specificembodiments thereof, it is apparent that many changes, modifications,and variations can be made without departing from the inventive conceptdisclosed herein. Accordingly, it is intended to embrace all suchchanges, modifications, and variations that fall within the spirit andbroad scope of the appended claims. All patent applications, patents,and other publications cited herein are incorporated by reference intheir entirety.

What is claimed is:
 1. Terpolymer containing 20 to 70 mole percent ofrepeating structural units of formula (I) and 3 to 40 mole percent ofrepeating structural units of formula (II): ##STR10## as well asrepeating structural units of formula (III): ##STR11## whereby Aindicates a direct single bond or a group of the formula: ##STR12## R₁indicates a hydrogen atom or a methyl group, R₂ indicates a 2-furanyloxyor 2-pyranyloxy group or a group of the formulas: ##STR13## R₃ indicatesa group of the formula:

    --CN

R₄ indicates a group selected from the groups of formulas: ##STR14## R₅indicates a C₁ -C₆ alkyl group or a phenyl group, R₆ indicates a C₁ -C₆alkyl group or a phenyl group, R₇ indicates a C₁ -C₆ alkyl group or aphenyl group, Y indicates a hydrogen atom or a methyl group, Z indicatesa group of the formula --OSi(CH₃)₃, m indicates 1, 2 or 3, n indicates 3minus m, and p indicates 0, 1, 2 or 3 and wherebyas many structuralunits of formula (III) are contained in the terpolymer such that itssilicon contents amounts to 7 to 20 weight percent.
 2. Terpolymeraccording to claim 1, whereby R₁ corresponds to a methyl group. 3.Terpolymer according to claim 1, whereby p amounts to 1, 2 or
 3. 4.Terpolymer according to claim 3, whereby p amounts to
 3. 5. Terpolymeraccording to claim 1, whereby R₂ corresponds to a group of the formulas:##STR15##
 6. Terpolymer according to claim 1, whereby R₂ corresponds toa group of the formula R₃ corresponds to a group of the formula --CNandR₄ corresponds to a group of the formula --(CH₂)₃ --Si[OSi(CH₃)₃ ]₃. 7.Terpolymer according to claim 1, containing 3-35 mole percent ofrepeating structural units of formula (II).
 8. Terpolymer according toclaim 6, containing 3-31 mole percent of repeating structural units offormula (II), 10 to 30 mole percent of repeating structural units offormula (III), whereby repeating structural units of formula (I) formthe balance to 100 mole percent.